Electrochemical timing apparatus

ABSTRACT

An electrochemical timing apparatus for a fuse or the like wherein a thin wire retaining a firing pin is located in an electrolytic solution spaced from a material of lower activity and a variable impedance is provided between wire and the material to control the rate of destruction of the wire by cathodic corrosion to compensate for the effects of ambient temperature on such rate of destruction.

United States Patent 1191 Schneider, Jr.

[ Feb. 19, 1974 ELECTROCHEMICAL TIMING APPARATUS [75] Inventor: Clayton J. Schneider, Jr., Elma,

[73] Assignee: Cornell Aeronautical Laboratory,

1nc., Buffalo, NY.

22 Filed: Dec. 23, 1971 21 Appl. No.: 211,206

[52] US. Cl 102/70.2, 102/16, 102/82 [51] Int. Cl. F42b 21/34, F42b 21/38 [58] Field of Search... 102/7, 8, 16, 18, 19.2, 70 R,

102/70 S, 70.2 R, 70.2 P, 70.2 A, 82, 86.2

[5 6] References Cited 2,526,670 10/1950 Kissinger et al. 102/16 3,175,055 3/1965 Klapheke 102/16 X 3,475,571 10/1969 Erwood 102/82 X Primary ExaminerBenjamin A. Borchelt Assistant Examiner-James M. Hanley Attorney, Agent, or FirmAllen J. Jaffe [5 7 ABSTRACT An electrochemical timing apparatus for a fuse or the like wherein a thin wire retaining a firing pin is located in an electrolytic solution spaced from a material of lower activity and a variable impedance is provided between wire and the material to control the rate of destruction of the wire by cathodic corrosion to compensate for the effects of ambient temperature on such rate of destruction.

12 Claims, 3 Drawing Figures PAIENIEUFEBIQIW I 3.792.663

VARIABLE IMPEDANC INVENTOR CLAYTON J. SCHNEIDER,JR.

ATTORNEY BACKGROUND OF THE INVENTION The present invention relates to electrochemical timing apparatus and, more particularly, to such apparatus employed in the actuation or fuzing of ordinance devices.

In the field of ordinance such as land mine implantation it is extremely important that devices unactuated by the enemy during warefare have a self-destruct function for protection against undesired ignitions. Thus, there is a need for a timing mechanism to reliably accomplish the self-destruct of ordinance devices such as land mines and demolition charges.

One type of timing mechanism that has been extensively used is the acid-wire timer in which the corrosive effect of an acid destroys a retaining wire and allows a firing pin to strike a primer. Although such timers are simple and inexpensive to construct, they are not reliable. This is due to the fact that time necessary to destroy the retaining wire is extremely dependent upon temperature. This dependence is so great that a given timer can exhibit a time ratio of more than ten to one over a relatively limited temperature range.

SUMMARY OF THE INVENTION The foregoing, as well as other, difficulties of prior devices are overcome according to the teachings of the present invention which provides a timing mechanism for ordinance devices that is simple, inexpensive and reliable.

Whereas the acid-wire timing mechanisms of the prior art rely on the uncontrolled acid destruction of the retaining wire, the timing mechanism of the present invention relies on the principle of controlled cathodic corrosion of the retaining wire.

The retaining wire is constructed of a relatively active metal and is housed in an electrolytic or corrosive fluid and cooperates with a second material constructed of a metal lower in activity than the retaining wire. An external electrical connection between the two metals is made through a temperature compensating circuit, the impedance of which controls the rate of material removal of the retaining wire. The temperature compensation circuit can be automatic to guarantee the time of destruction of the retaining wire or it can be influenced by an additional control for varying time periods for destruction, which adds greatly to the versatility of the device.

Basically the present invention provides an electrochemical timing apparatus which comprises; a housing, an electrolytic solution in the housing, retaining means in said solution for holding an actuator in one of two operative positions, the retaining means constructed of a relatively active material, a second material less active than the material of said retaining means in contact with said solution and spaced from the retaining means, and variable impedance means connecting the retaining means and the second material in series externally of said electrolytic solution whereby the rate of destruction of the retaining means and the release of the actuator to its second operative position is responsive to the impedance of the variable impedance means.

BRIEF DESCRIPTION OF THE DRAWING For a fuller understanding of the present invention reference should now be had to the following detailed description of the same taken in conjunction with the accompanying drawing, wherein;

FIG. 1 is a schematic cross-sectional view of the timing mechanism of the present invention;

FIG. 2 is a circuit diagram of typical variable impe' dance source employed in the device of FIG. 1; and

FIG. 3 is a circuit diagram of an alternative variable impedance source.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and, more particularly, to FIG. 1, the electrochemical timing apparatus is generally depicted by numeral 10 and comprises a.

generally cylindrical housing 12 which has suitably attached thereto a conventional fuse casing 14. Casing 14 contains a body of impact ignitable pyrotechnic or explosive 16 such as lead azide. A partition 18 physically separates and seals the interior chamber 20 of housing 12 from the interior chamber 22 of casing 14. Partition 18 has a central opening 24 for sealingly receiving a suitable elastomeric plug 26.

A striking pin 28, aligned with the ignitable material, is held in a first or cocked position by means of a thin wire or the like 30 attached at one end 32 to the pin 28, sealingly passing through plug 26 and affixed at its other end 33 to a conductive plug 34 of an end closure 36 of housing 12. The wire 30 normally holds pin 28 in its cocked position against the action of a suitable compression spring 38 interposed between plug 26 and a flange 40 of pin 28.

Wire 30 is constructed of a relatively active material, such as zinc whereas the walls of housing 12 are constructed of a material lower in activity, such as copper. A suitable electrolytic fluid 42 such as sodium hydroxide in water, substantially fills the interior of chamber 20. The type of electrolyte is not critical; almost any base or acid can be utilized. An external circuit is completed between wire 30 and housing wall 12 by means of lines 44 and 46 and a variable impedance source depicted generally at 48.

As illustrated in FIG. 2, the variable impedance source 48 may simply be a variable resistance 50.

In operation, the variable resistance is set to a value which is a function of the average ambient temperature conditions and functions to control the rate at which electrons travel from wire 30 to the less active material 12 through the variable impedance. In this manner the rate of cathodic corrosion or deplating the thin wire 30 is accurately controlled. When the corrosion of the wire 30 weakens it to the point where it breaks, pin 28 under the influence of spring 38 is allowed to travel towards and strike the primer or ignition material 16 causing a detonation or ignition as is well known. Thus, the resistance 50 is set to compensate for the relatively known average ambient temperature thereby preventing ambient temperature from unduly influencing the corrosion of the wire as would be the case with conventional acid-wire timers. For different known average ambient temperature conditions the value of resistance 50 would be difierently set.

Alternatively, as illustrated in FIG. 3, it is possible to employ an automatic temperature compensating circuit for controlling the rate of corrosion of wire 30. In this embodiment a resistance which varies in response to temperature, such as thermistor S2, is employed to automatically control the rate of cathodic corrosion of wire 30 in response to ambient temperature variations. In this manner the destruction time of wire 30 can remain substantially constant regardless of ambient temperature variations. Although thermistor 52 might be capable of functioning by itself to accomplish this constancy in destruction time, it has been found desirable to include the circuitry of FIG. 3 or its equivalent. In FIG. 3 the voltage applied to the base of transistor 54 via line 56 is proportional to ambient temperature as sensed by thermistor S2. The emitter to collector impedance across lines 44 and 46 is therefore proportional to ambient temperature and it is this impedance actually which is used to control the destruction rate of the wire 30. Variable resistances R, and R are provided to permit appropriate curve-shaping conductances for the response of the circuit, as is well known.

Although preferred embodiments of the present invention have been illustrated and described, changes will occur to those skilled in the art. It is therefore intended that the scope of thepresent invention is to be limited only by the scope of the appended claims.

I claim:

1. An electrochemical timing apparatus, comprising;

a. a housing,

b. an electrolytic solution in said housing,

c. retaining means in said solution for holding an actuator in one of two positions,

d. a second material less active than the material of said retaining means in contact with said solution and spaced from said retaining means, and

e. variable impedance means providing an electrical connection between said retaining means and said second material whereby the rate of destruction of said retaining means and by cathodic corrosion the release of the actuator to its second position is controlled by said variable impedance means.

2. The apparatus according to claim 1, wherein said electrical connection is externally of said electrolytic solution.

3. The apparatus according to claim 1, wherein said variable impedance means comprises a variable resistance.

4. The apparatus according to claim 1, wherein said variable impedance means is temperature responsive whereby increases in ambient temperature result in a decrease in the rate of destruction of said retaining means such that the time for destruction remains substantially constant.

5. The apparatus according to claim 1, wherein said retaining means comprises a relatively thin wire.

6. The apparatus according to claim 1, wherein said second material comprises the interior of said housing.

7. The apparatus according to claim 1, further comprising;

f. a fuse casing attached to said housing,

g. a body of pyrotechnic material located in said casing,

h. a firing pin adjacent to and normally spaced from said pyrotechnic material one end of which being held by said retaining means in said normally spaced position.

8. The apparatus according to claim 7, wherein said variable impedance means is temperature responsive whereby increases in ambient temperature result in a decrease in the rate of destruction of said retaining means such that the time for destruction remains substantially constant.

9. The apparatus according to claim 8, wherein said retaining means comprises a relatively thin wire.

10. The apparatus according to claim 9, wherein said second material comprises an interior wall of said housing.

11. The apparatus according to claim 7, wherein said retaining means comprises a relatively thin wire.

12. The apparatus according to claim 11, wherein said second material comprises an interior wall of said housing. 

1. An electrochemical timing apparatus, comprising; a. a housing, b. an electrolytic solution in said housing, c. retaining means in said solution for holding an actuator in one of two positions, d. a second material less active than the material of said retaining means in contact with said solution and spaced from said retaining means, and e. variable impedance means providing an electrical connection between said retaining means and said second material whereby the rate of destruction of said retaining means and by cathodic corrosion the release of the actuator to its second position is controlled by said variable impedance means.
 2. The apparatus according to claim 1, wherein said electrical connection is externally of said electrolytic solution.
 3. The apparatus according to claim 1, wherein said variable impedance means comprises a variable resistance.
 4. The apparatus according to claim 1, wherein said variable impedance means is temperature responsive whereby increases in ambient temperature result in a decrease in the rate of destruction of said retaining means such that the time for destruction remains substantially constant.
 5. The apparatus according to claim 1, wherein said retaining means comprises a relatively thin wire.
 6. The apparatus according to claim 1, wherein said second material comprises the interior of said housing.
 7. The apparatus according to claim 1, further comprising; f. a fuse casing attached to said housing, g. a body of pyrotechnic material located in said casing, h. a firing pin adjacent to and normally spaced from said pyrotechnic material one end of which being held by said retaining means in said normally spaced position.
 8. The apparatus according to claim 7, wherein said variable impedance means is temperature responsive whereby increases in ambient temperature result in a decrease in the rate of destruction of said retaining means such that the time for destruction remains substantially constant.
 9. The apparatus according to claim 8, wherein said retaining means comprises a relatively thin wire.
 10. The apparatus according to claim 9, wherein said second material comprises an interior wall of said housing.
 11. The apparatus according to claim 7, wherein said retaining means comprises a relatively thin wire.
 12. The apparatus according to claim 11, wherein said second material comprises an interior wall of said housing. 